Energy absorbing device and shoulder belt-type vehicle seats comprising such energy absorbing device

ABSTRACT

The invention relates to a vehicle seat for equipment with shoulder belts ( 24 ) connected to the seat backrest ( 21 ), comprising an energy absorbing device ( 1 ) acting on the seat backrest, wherein said energy absorbing device comprises deformable energy absorbing means ( 12 ), with at least one arcuate ( 13, 14 ) area of plastically fragmentable material, opposing the rotation of said seat backrest ( 21 ) with respect to a lower seat structure ( 20 ) in a first direction, corresponding to a forward-leaning movement of said seat backrest. The invention also relates to energy absorbing devices opposing the rotation of a first part ( 1 ) with respect to a second part ( 2 ) via deformable energy absorbing means ( 12 ) with an arcuate area ( 13, 14 ) of plastically fragmentable material, wherein the energy absorbing device comprises releasable retention means ( 16 ) subjecting every rotation of said first part with respect to said second part into a first direction to the reaction of said energy absorbing means and allowing the rotation of said first part with respect to said second part, into the direction opposite to said first direction, without acting on said energy absorbing means.

BACKGROUND OF THE INVENTION

The invention relates to a mechanical device designed to dissipatekinetic energy, such as (part of) the kinetic energy of a vehicle seat(in particular an aircraft passenger seat) and its occupant, wheninvolved in a survivable accident or incident (such as an emergencylanding of an aircraft).

More particularly the invention relates to such a device which can beused in connection with vehicle seats provided with shoulder belts.

The expression “vehicle seat” as used in the present text refers toseats that are appropriate for road or other surface transport vehiclesand for air transport vehicles; the vehicle seats to which the inventionmost suitably applies are seats for public transport vehicles andaircrafts.

Several energy absorbing systems for transport category aircraft seatshave been proposed in the art.

Most of the know systems are however designed to absorb the energy inthe underframe structure of the seat. Reference can for instance be madein this respect to the following patent publications: DE 440 57 53, GB2243540, U.S. Pat. No. 5,699,984, U.S. Pat. No. 5,069,505, U.S. Pat. No.4,861,103.

These known systems present serious drawbacks in view of the newstandards for seats in transport category aircrafts issued in June 1998by the U.S. Federal Aviation Administration (FAA) and the European JointAviation Authorities (JAA), to improve the chances of passenger survivalin emergency landing. Essentially the new rules are contained in theFAR/JAR 25-561/562. Of utmost importance to the background of thisPatent, is the section prescribing:

-   1. In § A and § B, the emergency landing conditions governing the    design of the seat and restraint system supposed to protect the    passengers.-   2. In § C, a set of performance pass/fail criteria, related to the    human body tolerance to impact loads, that must not be exceeded    during the dynamic tests conducted in accordance with § A and § B of    this section, in particular the Head Injury Criteria (HIC).

The above set of criteria for seats design is well known by the airtransport industry and aircrafts & seats manufacturers since June 1986.It appears however that the new performance standards prescribed in § Cdidn't receive appropriate attention.

Most of the redesign effort was focused on the seat structure to complywith the § A and § B, leaving the protection of the occupants to apatchwork of partial measures for most of the requirements of § C,resulting in no solution regarding the HIC, with however the exceptionof an inflatable lap belt system, derived from the air-bag technology,associated to a conventional seat structure.

According to the new rules, the former impact load required to besustained by the seat structure, and its tie-down to the floor, wasraised from a 9 g static load to a dynamic impact pulse triangularlyshaped, peaking at 16 g. To meet that condition, most seat manufacturersdeveloped various means to absorb part of the kinetic energy involved,in order to smooth off the peak of the 16 g pulse at a level acceptableby both the structure of the seat and its tie-down to the floor.

This process has however its limitations:

-   Because the space available between seat rows is limited, to protect    the egress path of the passengers in emergency conditions, the    maximum stroke allowed to the seat structure by any type of energy    absorption device is limited to 3 inches by the airworthiness    authorities.-   While this stroke might provide some smoothing off the peak dynamic    pulse, it has practically no effect on the occupant excursion.    Instead he will be allowed to pick-up speed relatively to the seat    or the bulkhead in front, resulting in a secondary impact of the    head which can be lethal.

In view of this, one approach to meet the new requirements will probablyinvolve the use of shoulder belt type passenger seats in transportcategory aircrafts.

Only few energy absorption systems have been proposed which can affectthe backrest of the seat and can therefore be used on such shoulder belttype passenger seats.

Thus, for instance, U.S. Pat. No. 6,209,955, involving a deformable backseat structure, U.S. Pat. No. 5,676,421 proposing multiple fragmentationpins on the back seat, U.S. Pat. No. 5,320,308 proposing a structural“breakover” device in association with a friction brake or clutcharrangement on the seat back, or EP 0 651 957 proposing a back seatstructure with damping structural parts.

DE 19648974 proposes a rather complex energy absorption device,involving torsion bars and breakable connecting pieces, to be used onthe underframe seat structure as well as at different levels of the backseat structure.

U.S. Pat. No. 4,688,662 on the other hand describes an energy absorbersystem on the interconnection of the seat bottom frame and the seat backframe The system utilises a pair of housings having facing cavities anda hollow deformable torsion member interconnecting the housings.

These state of the art energy absorption systems show several drawbackswith respect to the new criteria referred to above.

It is the object of the present invention to provide an absorptiondevice which meets the following objectives:

-   1. To restrain the passenger's body in the required dynamic    conditions by means of a shoulder harness, single or double,    featuring one or two attachments at the top of the frame of the    backrest, in association with a lap belt, as currently used in    automotive or other applications (such as aircraft applications),    -   comprising rotation means allowing the backrest to break over        when loaded forward by the shoulder belts, when the said loads        exert a momentum exceeding a predetermined static resistance        momentum on a specific part of the device. This component is        working directly against the pivot axis of the backrest and is        allowed a rotational, energy absorbing stroke, with the same        angular amplitude than the backrest breakover, under constant        application of the predetermined momentum;    -   to extend this protection to scenarios of successive impacts        including the full range of loading less than, and up to, the        ultimate required in a variety of directions, while keeping the        energy absorption capacity to smooth off the peak of the impact        pulses at the predetermined and built-in value.

To allow the return (or rebound) of the occupant to his initial raisedup position after each impact breakover.

-   2. To perform all functions in normal use by the passengers and    crew, in particular the control of the backrest recline as provided    for in conventional seats.    -   The backrest recline control device is characterised by its        integration with the breakover control system, working on the        same backrest axle, sharing the space available with the energy        absorption system in the breakover mode. Functionally the two        systems are independent and provisions are made to avoid any        interference in the range of designed angular motions of the        backrest, either in recline or in breakover.-   3. To provide for easy selection of recline and break-over angular    limitations, as required by the cabin layout, and current    regulations. Specific means to select the range of angular motions    are provided, for use by the maintenance crew.-   4. To make use of conventional technology in the design &    manufacturing.-   5. To design for the lowest possible weight and production cost-   6. To design for a minimum maintenance cost-   7. To be compatible with a conventional seat configuration & its    installation in a current, pressurised, transport category aircraft

SUMMARY OF THE INVENTION

The invention thus provides for a vehicle seat for equipment withshoulder belts connected to the seat backrest, comprising an energyabsorbing device acting on the seat backrest, in which said energyabsorbing device comprises deformable energy absorbing means (12), withat least one arcuate (13,14) area of plastically fragmentable material,opposing the rotation of said seat backrest (21) with respect to a lowerseat structure (20) in one direction, corresponding to a forward-leaningmovement of said seat backrest.

The concept of deformable energy absorbing means comprising arcuateareas of plastically fragmentable material is known per se in the priorart, in connection with energy absorption on safety belt retractor meansand/or retention means. Reference is made in this respect to prior artdocuments U.S. Pat. No. 5,639,806 and EP 1 000 822.

According to a preferred embodiment of the invention, said deformableenergy absorbing means preferably comprise

at least one disc with at least one radially positioned arcuate area ofplastically fragmentable material, and

at least one stop plug acting upon said arcuate area of fragmentablematerial in said disc.

According to a more preferred embodiment of the invention, said disc(s)comprise at least two radially positioned arcuate areas of plasticallyfragmentable material, and at least two corresponding stop plugs;

most preferably the energy absorbing means comprise two discs and (or)two to four radially positioned arcuate areas of plasticallyfragmentable material, each extending over an angle of, for instance,0,4 to 3 radiant (approximately 24–180°), and two to four correspondingstop plugs. Depending on the specific application the arcuate areas ofplastically fragmentable material may however extend over a smallerangle (as from 0,1 radiant or less), or over a larger angle.

The plastically fragmentable material of the arcuate fragmentation areasis preferably selected from aluminium, aluminium alloy 2024 T3,aluminium alloy AU4G1, or any other metal, synthetic or compositematerial having equivalent properties.

A very specific embodiment of the invention may involve an energyabsorbing device comprising a first part connected to the lower seatstructure, respectively to the lower portion of the seat backrest,rotably interconnected with a second part connected to the lower portionof the seat backrest, respectively to the lower seat structure, via saiddeformable energy absorbing means, whereas the axis of rotation of saidrotably interconnected first part and second part is positionedsubstantially along or in the vicinity of the hip joint axis in theprofile of an average occupant.

According to an interesting embodiment of the invention, releasableretention means may be provided between such first part (2) and suchsecond part (4), allowing the rotation of said first part with respectto said second part means into the direction opposite to said onedirection, corresponding to a backward-leaning direction of the seatbackrest, without acting on said energy absorbing means, whereas therotation of said first part with respect to said second part into saidone direction is subjected to the reaction of said energy absorbingmeans.

According to a preferred feature of this embodiment of the invention,said first part and said second part respectively constitute

a support means of the lower seat structure, and

a shaft connected to the lower portion of the seat backrest

(or vice versa), whereas said releasable retention means preferablycomprise a ratchet wheel mechanism providing fixed connection of saidshaft with respect to said deformable energy absorbing means in saidfirst direction, while providing free rotation of said shaft withrespect to said deformable energy absorbing means in said oppositedirection.

Said shaft preferably comprises a grooved part interconnecting saidshaft to a corresponding grooved aperture in said deformable energyabsorbing means, said releasable retention means, said disc(s) withradially positioned arcuate area(s) of plastically fragmentable materialand/or said ratchet wheel mechanism.

According to a further feature of the invention, a separate conventionalbackrest recline control may in addition be integrated into said energyabsorbing device, whereas said disc(s) with one or more area(s) ofplastically fragmentable material further comprise one or morecorresponding radially positioned arcuate open areas, allowing rotationof the disc(s) from a referenced position, defined with the backrest inupright position, into a direction opposite to the arcuate area ofplastically fragmentable material. The slot width of said arcuate openarea should suitably be slightly larger than the diameter of the stopplug to allow free rotation in the backward-leaning direction, withoutacting on the energy absorbing means nor making use of the releasableretention means.

The seat preferably comprises one energy absorbing device at one side ofthe seat, whereas the seat backrest is interconnected, on thecorresponding side of the seat, to said energy absorbing device via agrooved shaft, and, on the other side of the seat to the energyabsorbing device of the adjacent seat or the seat structure, via a freerotating axle.

The type of vehicle seats to which the invention most suitably appliesis the group comprising surface transport vehicle seats, publictransport vehicle seats and air transport vehicle seats.

It has further been found that in the vehicle seat according to theinvention, the axis of rotation of the backrest has preferably to bemoved forward to avoid the bulk of the energy absorbing deviceprotruding beyond the rear envelope of the seat. This position isdifferent from the current position of the reclining axis onconventional seats which are mostly located in the vicinity of thebackrest frame.

Resulting from this position of the backrest rotation axis, to makeprovision for passenger comfort in the lower back area, the support axleis preferably split in two parts on the left and right side of thebackrest frame, thus avoiding to install an axle crossing the full widthof the backrest. This configuration leads to concentrate the momentum ofthe backrest to one side of the frame engaged through the axle of theenergy absorbing device, the other side being a free rotation axle withno momentum capacity. This design decision, resulting in one energyabsorbing unit per backrest, has proved to be the most economical inweight and cost, as well as compatible with the curved shape of apressurised aircraft cabin, forbidding installation of an energyabsorbing device on outboard seats in most seating layouts.

One of the additional design objectives of the invention is to provide abackrest control device with a dual capability:

-   -   In normal use, to control the recline at the choice of the        passenger,    -   In emergency use, to control the breakover by a preset energy        absorbing device.

-   1. To save space and weight, the energy absorbing device according    to the invention combines the two functions in one device as compact    as possible, located under the armrest, working on the common axle    in connection with the backrest frame.

This offset position of the axle a positive effect on the safety andcomfort of the passenger.

Indeed, in this position, the axis of rotation of the backrest frame iscloser to the natural body hip joint than in conventional seats. As aresult, when reclining for comfort, or breaking-over for safety, therotation of the upper torso matches closely the rotation of the backrestand avoids uncomfortable back friction in recline, while keeping theinitial shoulder belt position in break-over conditions.

As a further bonus, for maintenance purpose, it appears that the offsetposition of the backrest axle offers an easy access when dismounting thebackrest from the seat main frame. To that end the axle of the backrest,featuring longitudinal grooves to transfer all momentum controlling thebackrest angle, may allow, by axial motion, an easy disassembling of thebackrest from the main seat frame.

This feature is also partially used for allowing a full breakover whenrequired by a stretcher installation.

As the arcuate area, expected to absorb energy of a single impact,corresponds to the angular rotation of the back-rest during applicationof the impact loads, and as this rotation is limited to an anglematching the available striking distance ahead of the occupant, itresults that the angular capacity of the arcuate area is from three tofour times the capacity needed to absorb a single impact.

The energy absorbing mechanism according to the invention can thereforebe designed to use this redundant capacity to cope with successiveimpacts scenarios.

Introducing a ratchet wheel in between the backrest and the discssupporting the arcuate area, allows the rebound of the backrest whilekeeping the disc in the position reached by the previous impact.

Ipso facto, the return of the backrest to its initial upright positionmeets the requirement limiting the breakover, and/or permanentdeformation, especially when the seat would be installed next to anemergency exit.

This capacity to return to initial position and be available for asecond or a third impact, is a distinctive advantage of the deviceaccording to the invention over the inflatable lap belt or any type ofenergy absorbing devices working on the seat structure.

The axis of rotation of the seat backrest is therefore preferablypositioned substantially along or in the vicinity of the hip joint axisin the profile of an average occupant (i.e. the men and woman 50% ileoccupant, well known in the art).

The energy absorbing device described above has a triple function in thevehicle seats according to the invention:

-   -   absorption of the energy on the base structure of the seat;    -   control of the headpath excursion of the head and upper body of        the occupant    -   reduction of the deceleration applied to the upper body part of        the passenger.

The invention also relates to an energy absorbing device, per se,designed to oppose the rotation of a first part with respect to a secondpart via deformable energy absorbing means with an arcuate area ofplastically fragmentable material, wherein the energy absorbing devicecomprises releasable retention means subjecting every rotation of saidfirst part with respect to said second part support means into saidfirst direction to the reaction of said energy absorbing means, andallowing the rotation of said first part with respect to said secondpart into the direction opposite to said first direction, without actingon said energy absorbing means.

According to a preferred embodiment of the energy absorbing deviceaccording to the invention, said deformable energy absorbing meanscomprise

at least one disc with at least one radially positioned arcuate area ofplastically fragmentable material, and

at least one stop plug acting upon said arcuate area of fragmentablematerial in said disc.

The disc(s) preferably comprise at least two radially positioned arcuateareas of plastically fragmentable material and at least twocorresponding stop plugs; the energy absorbing means may for instancecomprise two discs with each two to four radially positioned arcuateareas of plastically fragmentable material, each extending over an angleof 0,4 to 3 radiant, and two to four corresponding stop plugs. Dependingon the specific application the arcuate areas of plasticallyfragmentable material may however extend over a smaller angle (as from0,1 radiant or less), or over a larger angle.

The plastically fragmentable material is preferably selected fromaluminium, aluminium alloy 2024 T3, aluminium alloy AU4G1, or any othermetal, synthetic or composite material having equivalent properties.

According to another preferred feature of the energy absorbing deviceaccording to the invention, said first part and said second partconstitute a support means and a shaft, whereas said releasableretention means comprise a ratchet wheel mechanism providing fixedconnection of said shaft with respect to said deformable energyabsorbing means in said first direction, while providing free rotationof said shaft with respect to said deformable energy absorbing means insaid opposite direction.

According to still another preferred feature of the invention, saidshaft comprises a grooved part interconnecting said shaft to acorresponding grooved aperture in said deformable energy absorbingmeans, said releasable retention means, said disc(s) with radiallypositioned arcuate area(s) of plastically fragmentable material and/orsaid ratchet wheel mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A & 1 B : Isometric view of a typical assembly of a backrest andthree point shoulder harness, mounted on a seat structure via a groovedshaft on one side and a free rotation axis on the opposite side. Thegrooved shaft is engaged in the energy absorbing device according to theinvention. FIG. 2: Isometric view of the energy absorbing deviceaccording to the invention. FIG. 3: Exploded view of the energyabsorbing device according to the invention. FIG. 4: Side view of a discassembly containing a disc, a ratchet wheel, 3 ratchets, ratchet axlesand springs; the arcuate area divided in the energy absorbing semicircular path and the free recline slot, separated by the static stopplug FIG. 5: Side view of a disc showing the configuration during theforward impact, when the disc rotate and the material of the arcuatearea is fragmented by the static stop plug FIG. 6: Isometric viewdescribing the configuration of the discs components during the reboundphase after the forward initial impact FIG. 7: Isometric view showingthe configuration of the recline control sub-assembly during thebackrest recline function

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of a preferred embodiment of theinvention, as illustrated in the attached drawings.

It will ompbe appreciated by anyone skilled in the art that manymodifications and variations of the invention are possible in the lightof the above teaching and within the boundaries of the appending claims,without departing from the general scope and spirit of the invention.

The energy absorbing device according to this embodiment of theinvention, for use on an aircraft passenger seat, involves:

A casing (the support means referred to above), in the general shape ofa flat cylinder containing the working parts of the energy absorbingfunction, including essentially a grooved shaft extending transverselyin the adjacent backrest frame to engage in the internally groovedsection of the adjacent backrest bracket, to form a rigid connection intorsion between the backrest frame and the energy absorbing device. Eachcasing is also rigidly fixed to the seat bottom frame.

Inside the casing, the grooved shaft engages one disc (or wheel),featuring matching internal grooves, to the effect that the discs willbe forced by the grooved shaft to follow all angular rotations, inrecline or breakover of the backrest.

At the periphery of the discs (or wheels), an arcuate path is providedin a semi circular shape about the shaft axis. In this path, thematerial is reduced in thickness to leave a relatively thin webfeaturing a limited strength, dedicated to absorb energy by materialfragmenting process, when forced against a static stop plug inserted ata specific point perpendicular and through the disc in the arcuateprovided area.

The said static stop plug, mounted parallel to the shaft, is of suchlength as to extend through the casing at both ends after closure of thecasing cover plates.

In this position the plug will oppose a firm stop to the rotation of thedisc in the direction and under impulse of the backrest breakover.

In the opposite direction, corresponding to the backrest recline, thedisc is free to rotate as the concerned area has been open to rotationby a curved arcuate slot whose width exceed the diameter of the staticstop plug. The designed arc of the slot is such as to allow the maximumdesigned recline angle that the occupant of the seat might wish to adoptby use of a conventional control.

The breakover area features a restriction to the disc, and theassociated backrest, in the breakover rotation. This restriction couldbe a reduced width, smaller than the diameter of the static stop plug,or a web of limited thickness, or a combination of both, tuned toprovide by the resistance of the stop plug, a semi circular path opposedto the rotation of the backrest up to a predetermined value of thebreakover momentum. When this value is exceeded by the impactsconditions the disc start to rotate and absorb energy by materialfragmenting.

The energy absorbing system of this example in particular involves aplurality of discs mounted in parallel on a common shaft connected toone individual backrest.

They are similarly provided in the arcuate area, to propose each a freeslot for backrest recline and a reduced thickness slot for energyabsorption by material fragmenting process. The stop plug is installedthe same way, through all discs and the casing static support, toperform the same stopping function.

The energy absorbing system of the example in particular also comprisestwo static plugs mounted in parallel with the shaft, positioneddiametrically opposed in the arcuate area and sharing equally theavailable arcs dedicated for clearing the recline on one side and absorbthe energy, on the other side, as required by the operational and orimpact conditions.

The energy absorbing system according to this example furthermorecomprises a ratchet wheel, installed between the shaft and each one ofthe discs, so that the torque applied by the breakover of the backrestis transmitted to the discs by a set of spring loaded ratchets.

In the energy absorbing system according to the example, the dimensionsof the “forced slots” in the breakover area of the discs, are such that,after an impact, the discs will be retained by jamming on the staticplugs in the position reached at the end of the impact pulse. In thissituation, the ratchet wheels will enable the backrest to return to itsinitial upright position, and the system will be ready to perform thesame function of energy absorption, starting from the new position ofthe discs.

In the energy absorption system according to the example, the total arcprovided for energy absorption, has a capacity to absorb a succession ofbreakover impacts amounting, for example, to three impacts using each anaverage arc of 30°, up to a total of 90° arc.

The energy absorption system according to the example, comprises twodiscs, mounted in parallel on the common shaft, allowing installation ofa recline control lever in between, in selective association with thecommon shaft, to allow control of the recline of the backrest by theoccupant of the seat. The selective association is meant to control therecline only while leaving the possibility for backrest breakoverwithout the angular limitations of a conventional recline system.

In the following description, any element identified by a number in onedrawing will represent the same element in any other drawing. Thefollowing is a list of the major working elements:

-   Energy absorbing device assembly (1)-   Casing (2)-   Casing cover (3)-   Grooved shaft (4)-   Free rotation axle (5)-   Disc (or discs) chamber (6)-   Recline control sub-assy (7)-   Recline lever (8)-   Recline transmission wheel (9)-   Breakover control sub-assy (10)-   Disc sub-assy (11)-   Disc frame & arcuate area (12)-   Disc arcuate energy absorbing section (13)-   Disc arcuate material area fragmented during impact (14)-   Disc arcuate recline slot section (15)-   Ratchet wheel (16)-   Ratchets & axles (17)-   Ratchet springs & axles (18)-   Static stop plug (19)-   Seat primary structure (20)-   Backrest structure assembly (21)-   Backrest controlled rotation bracket (22)-   Backrest free rotation bracket (23)-   Shoulder harness assembly (24)-   Diagonal shoulder belt (25)-   Casing opening for recline lever (26)-   Lug (casing internal extension) (27)-   Angular gaps in recline control assembly (28)-   Grooved shaft lateral stop cover (29)

For the convenience of description, a forward direction and a rearwarddirection are defined by corresponding arrows relative to theperspective of a person sitting normally in passenger seat.

The device (1) is a mechanical rotative energy absorbing device,designed to dissipate part of the kinetic energy of the occupant of apassenger's seat, in a Transport Category Aircraft, when decelerated ina forward dynamic impact.

The device is fixed to the seat primary structure (20) and works inassociation with a backrest structure (21) on which a shoulder belt(25), is attached.

The shoulder belt (25) is associated with a lap belt (26) as parts of athree point shoulder harness assy (24) (ref. to FIG. 1).

The device controls the use, as a stopping distance, of the spaceavailable for breakover in front of the occupant, to the effect that theoccupant head path in the direction of forward inertial load will bereduced and to avoid any lethal contact with any aircraft interiorpartition or seat in front, or any other interior feature.

The device is working, via the grooved shaft (4), through the structureof the backrest (21) and the shoulder belt (25), in opposition to anyforward motion of the upper torso of the occupant, and will limit theloads applied to the mass of the upper torso within acceptable humanbody tolerance, considering the energy level involved, and will alsolimit the loads in the lower seat structure (20), including the tie-downto the aircraft floor and the aircraft floor itself, within allowablevalues.

The backrest structure is also pivotally connected by a free rotationbracket (23) to the free rotation axle (5) on the side opposite to thedevice (ref. to FIG. 2).

The energy absorbing function is performed in a break-over controlsub-assy (11) making use of a “fragmented material process” designed toproduce an initial predetermined locking momentum on the grooved shaft(4) of the backrest bracket (22), therefore opposed to the backrestrotation up to a predetermined level, followed by a continuous brakingmomentum at a slightly superior level.

The energy absorbing device (ref. to FIG. 3) is characterised by acasing (2), in the general shape of a flat cylinder containing in thedisc chamber (6) the working parts of the energy absorbing function,including essentially a grooved shaft (4) extending transversely in theadjacent backrest frame to engage in the internally grooved section ofthe adjacent backrest bracket (22), to form a rigid connection intorsion between the backrest frame (21) and the energy absorbing device(1). The grooved shaft (4) is fixed laterally to the grooved backrestbracket (22) by a stop cover (29).

The casing (2) is also rigidly fixed to the seat primary structure (20).

Inside the casing, the grooved shaft (4) engages, via a ratchet wheelsystem (16) featuring internal grooves and associated set of minimumthree ratchets spring loaded (18) pivotally connected to the disc frames(12) in one or several discs sub-assy (11), to the effect that the discssub-assy (11) will be forced by the grooved shaft to follow allrotations of the backrest in recline or breakover, with the exception ofthe rebound post-impact.

At the periphery of the discs sub-assy (11), an arcuate area (12) isprovided in a semi circular ring about the shaft axis. This area isdivided in two sections: One section (13) is in charge of the energyabsorbing function. In this section, the material is reduced inthickness to leave a relatively thin web featuring a limited strength,designed to absorb energy by material fragmenting process, when forcedagainst a static stop plug (19) inserted at a specific pointperpendicular and through the disc in the arcuate provided area (12)(ref. to FIG. 5).

In the preferred embodiment, for a better balance of the momentum loads,two static stop plugs (19) are mounted in parallel to the shaft (4),diametrically opposed, through the arcuate area and sharing equally theavailable arcs dedicated for clearing the recline on one way and absorbthe energy, on the other way, as required by the operational and orimpact conditions.

The said static stop plugs (19), mounted parallel to the shaft, are ofsuch length as to extend through the casing, through any lug (27) orcasing internal extension provided in between the discs and at both endsin the casing cover plates (3).

In this position the plugs will oppose a firm stop to the rotation ofthe disc sub-assy (11) in the direction and under impulse of thebackrest breakover and will transfer any breakover momentum to thecasing (2) and to the seat primary structure (20).

The arcuate area (13) opposes a restriction to the disc, and theassociated backrest, to the breakover rotation. This restriction couldresult from a reduced width, smaller than the diameter of the staticstop plug (19), or a web of limited thickness, or a combination of both,tuned to provide against the resistance of the stop plug, a semicircular path opposed to the rotation of the backrest up to apredetermined value of the breakover momentum. When this value isexceeded by the impacts conditions the disc start to rotate and absorbenergy by material fragmenting.

A ratchet wheel (16) is installed between the shaft and each one of thediscs, so that the torque applied by the breakover of the backrest istransmitted to the discs by a set of spring loaded ratchets (17) (ref.to FIG. 4). This one-way momentum transmission allows the return of thebackrest close to its initial pre-impact position, to meet therequirements regarding the allowable post-impact seat structuredeformation.

The device is also designed to perform its energy absorbing function inresponse to successive impacts, as might be expected in a survivableemergency landing scenario, by allowing, after each impact, the returnof the occupant to his initial upright position and offering adequatecapacity for further energy absorbing strokes.

Indeed the arcuate area (13), expected to absorb energy of a singleimpact, corresponds to the angular rotation, or breakover, of thebackrest during application of a single impact load, and as thisrotation is, by the seat installation criteria in an aircraft, limitedto an angle matching the available stopping distance in front of theoccupant (about 25°), it may be observed that the angular capacity ofthe arcuate area being 120° is from three to four times the capacityneeded to absorb a single impact at the highest designed level (16Gforward).

This being a direct advantage resulting from the internal geometry ofthe device, that is, the compact semi circular shape of the arcuate area(13), the device mechanism is designed with the means to use thisredundant capacity to cope with successive impacts scenarios.

By making use of the ratchet wheels (16) (provided in between the shaft(4) of the backrest and the discs sub-assy (11) supporting the arcuatearea (12) to allow the rebound of the backrest), it is provided in thedetail design of the arcuate area (13) the possibility to keep the discssub-assy (11) in the position reached under the previous impact (ref. toFIG. 6).

To that end, the dimensions of the forced slots in the breakover area ofthe discs (14), are such that, after an impact, the discs will beretained by jamming on the static plugs in the position reached at theend of the impact pulse. In this situation, the ratchet wheels willenable the backrest to return to its initial upright position, and thesystem will be ready to perform the same function of energy absorption,starting from the new position of the discs.

This capacity to return to initial position and be available for asecond or a third impact, is a distinctive advantage of the device overthe inflatable lap belt or any type of energy absorbing devices workingon the seat structure

Besides, designing the arcuate energy absorption section to limit thestroke to about 25° under a 16 g impact is a challenging designobjective in consideration of the occupant tolerance and the seatstructural limitations. The experience has shown that the margin ofsuccess on this criteria is very narrow but not out of reach to thosefamiliar with the art to which this invention relates.

There is also a dual capability of the backrest control device. Due tothe particular configuration of the backrest pivot point, it was soondetermined that one of the design objective of the invention should beto provide a backrest control device with a dual capability:

-   in normal flight conditions, to control the recline at the choice of    the passenger;-   in emergency conditions, to control the breakover by a pre-set    energy absorbing device;

To save space and weight, it was decided to combine the two functions inone assembly (1), as compact as possible, located under the armrest,working on the common shaft in connection with the backrest frame.

The assembly (1) integrates the means to allow the occupant of the seatto control the recline of his backrest.

The backrest linear recline control device (19) is characterised by itsintegration with the breakover control system, working on the samebackrest shaft (4) sharing the space available in the disc chamber (6)with the energy absorption system

Functionally the two systems are independent and provisions are made toavoid any interference in the range of designed angular motions of thebackrest, either in recline or in breakover.

They are similarly provided in the arcuate area (22), to propose each afree arcuate recline slot section (15) for backrest recline opposite tothe energy absorbing section (13). The stop plugs (19) are installed thesame way, through all discs and the casing static support, to performthe same stopping function in the upright position of the backrest.

The two discs are mounted in parallel on the common shaft (4), allowinginstallation of a recline control lever (8) in between, in selectiveassociation with the common shaft, to allow control of the recline ofthe backrest by the occupant of the seat. The selective association ismeant to control the recline only while leaving the possibility forbackrest breakover without the angular limitations of a conventionalrecline system. This is achieved by installation of a selectivetransmission wheel (9) in between the shaft and the recline lever (8).Angular gaps (28) are provided between the wheel (9) and the lever (8),allowing the necessary breakover as required by the energy absorbingfunction without interference (ref. to FIG. 7).

For the same purpose, In the opposite direction, corresponding to thebackrest recline, the discs sub-assy (11) are free to rotate as theconcerned area has been opened to rotation by the arcuate recline slot(15) whose width exceed the diameter of the static stop plug (19). Thedesigned arc of the slot is such as to allow the maximum designedrecline angle that the occupant of the seat might wish to adopt by useof a conventional linear control.

While specific embodiments and applications of this invention have beenshown and described, it should be clear to those skilled in the art thatmany more modifications and applications are possible without departingfrom the inventive concepts herein.

Thus, whereas the invention has been illustrated specifically referringto aircraft seats, it must be stressed that the invention is alsoparticularly suited for any type of surface or air transport vehicle,and in particular for any type of public transport vehicle.

The invention is, therefore, not to be restricted in any way, except inthe spirit of the appended claims.

1. Vehicle seat for equipment with shoulder belts connected to a seatbackrest (21) wherein an energy absorbing device (1), acting on the seatbackrest, comprises deformable energy absorbing means (12), with atleast one arcuate area (13, 14) of plastically fragmentable material,opposing the rotation of said seat backrest (21) with respect to a lowerseat structure (20), in one direction, corresponding to aforward-leaning movement of said seat backrest, a first part (2),connected to the lower seat structure (21), respectively to the lowerportion of the seat backrest (20), being rotably interconnected, viasaid deformable energy absorbing means (12), with a second part (4),connected to the lower portion of the seat backrest (20), respectivelyto the lower seat structure (21), whereas releasable retention means(16) are provided between said first part (2) and said second part (4),allowing the rotation of said first part with respect to said secondpart into the direction opposite to said one direction, corresponding toa backward-leaning direction of the seat backrest, without acting onsaid energy absorbing means, whereas the rotation of said first partwith respect to said second part into said one direction is subjected tothe reaction of said energy absorbing means.
 2. Vehicle seat accordingto claim 1, wherein said first part (2) and said second part (4)respectively constitute a support means (2) of the lower seat structureand a shaft (4) connected to the lower portion of the seat backrest, orvice versa, whereas said releasable retention means comprise a ratchetwheel mechanism providing fixed connection of said shaft with respect tosaid deformable energy absorbing means in said first direction, whileproviding free rotation of said shaft with respect to said deformableenergy absorbing means in said opposite direction.
 3. Vehicle seataccording to claim 2, wherein said deformable energy absorbing meanscomprise at least one disc with at least one radially positioned arcuatearea of plastically fragmentable material, and at least one stop plugacting upon said arcuate area of fragmentable material in said disc. 4.Vehicle seat according to claim 2, wherein said deformable energyabsorbing means comprise at least one disc with at least two radiallypositioned arcuate areas of plastically fragmentable material, and atleast two corresponding stop plugs acting upon said arcuate area offragmentable material in said disc.
 5. Vehicle seat according to claim2, wherein the axis of rotation of said rotably interconnected firstpart (2) and second part (4) is positioned substantially along or in thevicinity of the hip joint axis in the profile of an average occupant. 6.Vehicle seat according to claim 2, wherein a backrest recline control isintegrated into said energy absorbing device, whereas said disc(s) withone or more area(s) of plastically fragmentable material furthercomprise one or more corresponding radially positioned arcuate openareas, allowing rotation of the disc(s) from a referenced position,defined with the backrest in upright position, into a direction oppositeto the arcuate area of plastically fragmentable material.
 7. Vehicleseat according to claim 2, wherein the seat comprises one energyabsorbing device at one side of the seat, whereas the seat backrest isinterconnected, on the corresponding side of the seat, to said energyabsorbing device via a grooved shaft, and, on the other side of the seatto the energy absorbing device of the adjacent seat or the seatstructure, via a free rotating axle.
 8. Vehicle seat according to claim2, wherein said vehicle is a public transport vehicle.
 9. Aircraft seatfor equipment with shoulder belts connected to a seat backrest (21)wherein an energy absorbing device (1), acting on the seat backrest,comprises deformable energy absorbing means (12), with at least onearcuate area (13, 14) of plastically fragmentable material, opposing therotation of said seat backrest (21) with respect to a lower seatstructure (20), in one direction, corresponding to a forward-leaningmovement of said seat backrest, a first part (2), connected to the lowerseat structure (21), respectively to the lower portion of the seatbackrest (20), being rotably interconnected, via said deformable energyabsorbing means (12), with a second part (4), connected to the lowerportion of the seat backrest (20), respectively to the lower seatstructure (21), whereas releasable retention means (16) are providedbetween said first part (2) and said second part (4), allowing therotation of said first part with respect to said second part into thedirection opposite to said one direction, corresponding to abackward-leaning direction of the seat backrest, without acting on saidenergy absorbing means, whereas the rotation of said first part withrespect to said second part into said one direction is subjected to thereaction of said energy absorbing means.
 10. Aircraft seat according toclaim 9, wherein said first part (2) and said second part (4)respectively constitute a support means (2) of the lower seat structureand a shaft (4) connected to the lower portion of the seat backrest, orvice versa, whereas said releasable retention means comprise a ratchetwheel mechanism providing fixed connection of said shaft with respect tosaid deformable energy absorbing means in said first direction, whileproviding free rotation of said shaft with respect to said deformableenergy absorbing means in said opposite direction.
 11. Aircraft seataccording to claim 10, wherein said deformable energy absorbing meanscomprise at least one disc with at least one radially positioned arcuatearea of plastically fragmentable material, and at least one stop plugacting upon said arcuate area of fragmentable material in said disc. 12.Aircraft seat according to claim 10, wherein said deformable energyabsorbing means comprise at least one disc with at least two radiallypositioned arcuate areas of plastically fragmentable material, and atleast two corresponding stop plugs acting upon said arcuate area offragmentable material in said disc.
 13. Aircraft seat according to claim10, wherein the axis of rotation of said rotably interconnected firstpart (2) and second part (4) is positioned substantially along or in thevicinity of the hip joint axis in the profile of an average occupant.14. Aircraft seat according to claim 10, wherein a backrest reclinecontrol is integrated into said energy absorbing device, whereas saiddisc(s) with one or more area(s) of plastically fragmentable materialfurther comprise one or more corresponding radially positioned arcuateopen areas, allowing rotation of the disc(s) from a referenced position,defined with the backrest in upright position, into a direction oppositeto the arcuate area of plastically fragmentable material.
 15. Aircraftseat according to claim 10, wherein the seat comprises one energyabsorbing device at one side of the seat, whereas the seat backrest isinterconnected, on the corresponding side of the seat, to said energyabsorbing device via a grooved shaft, and, on the other side of the seatto the energy absorbing device of the adjacent seat or the seatstructure, via a free rotating axle.